Fix todo!() errors in legacy client (#28)

Replace the todo!() with relevant errors from hyper::Error

Author: film42

src/client/legacy.rs

@@ -58,6 +58,7 @@ pub struct Error {
 #[derive(Debug)]
 enum ErrorKind {
     Canceled,
+    ChannelClosed,
     Connect,
     UserUnsupportedRequestMethod,
     UserUnsupportedVersion,
@@ -686,7 +687,7 @@ impl<B> PoolClient<B> {
     ) -> Poll<Result<(), Error>> {
         match self.tx {
             #[cfg(feature = "http1")]
-            PoolTx::Http1(ref mut tx) => tx.poll_ready(cx).map_err(|_| todo!()),
+            PoolTx::Http1(ref mut tx) => tx.poll_ready(cx).map_err(Error::closed),
             #[cfg(feature = "http2")]
             PoolTx::Http2(_) => Poll::Ready(Ok(())),
         }
@@ -739,23 +740,23 @@ impl<B: Body + 'static> PoolClient<B> {
             #[cfg(feature = "http2")]
             PoolTx::Http2(ref mut tx) => Either::Right(tx.send_request(req)),
         }
-        .map_err(|_| todo!());
+        .map_err(Error::tx);
 
         #[cfg(feature = "http1")]
         #[cfg(not(feature = "http2"))]
         return match self.tx {
             #[cfg(feature = "http1")]
             PoolTx::Http1(ref mut tx) => tx.send_request(req),
         }
-        .map_err(|_| todo!());
+        .map_err(Error::tx);
 
         #[cfg(not(feature = "http1"))]
         #[cfg(feature = "http2")]
         return match self.tx {
             #[cfg(feature = "http2")]
             PoolTx::Http2(ref mut tx) => tx.send_request(req),
         }
-        .map_err(|_| todo!());
+        .map_err(Error::tx);
     }
     /*
     //TODO: can we re-introduce this somehow? Or must people use tower::retry?
@@ -1456,4 +1457,8 @@ impl Error {
     fn tx(src: hyper::Error) -> Self {
         e!(SendRequest, src)
     }
+
+    fn closed(src: hyper::Error) -> Self {
+        e!(ChannelClosed, src)
+    }
 }